T-wave alternans (TWA) is beat-to-beat alternation in the morphology, amplitude, and/or polarity of the T-wave, and can be observed on surface electrocardiogram (ECG) recordings. TWA has been recognized in a variety of clinical conditions, including acquired and congenital long QT syndrome and ischemic heart disease, and has been found to be associated with ventricular arrhythmias. TWA is considered an independent predictor for cardiac arrhythmias. Experimentally, TWA has been shown to be a precursor of ventricular tachycardia.
In past practice, TWA has been assessed from surface ECG recordings obtained in a clinical setting as an indication of the long-term risk for ventricular arrhythmias. A Fast Fourier Transform (FFT) method is used for frequency domain analysis of T-waves, and a Modified Moving Averaging (MMA) method is used for time domain analysis of T-waves. The low-amplitude changes in the T-wave signal during TWA, which is on the order of microvolts, requires complicated software to assess TWA from a surface ECG recording of typically 128 heart beats or more during exercise or high-rate atrial pacing when using the FFT method. A need remains for TWA assessment and monitoring in implantable medical devices for identifying patients at high risk for ventricular arrhythmias and sudden cardiac death.